In European Pat. Appl. No. 31.041, there are described, amongst others, also certain pyrethroid insecticides falling under the following general formula: ##STR1## wherein: R.sup.1 =F, Cl, Br, CF.sub.3 ;
R.sup.2 =F, Cl, Br; PA1 R.sup.5 =H, CN, C.tbd.CH
The preparation of the compounds of formula I is carried out starting from cyclopropanecarboxylates intermediates of formula: ##STR2## (wherein: R=OH, a C.sub.1 -C.sub.4 alkoxy, a halogen, while R.sup.1 and R.sup.2 have the meanings given in general formula I).
For the synthesis of the compounds of formula I, the esters of formula II in which R=alkoxy, are hydrolyzed to the corresponding free acids (II, R=OH) and converted to the corresponding acyl halides (II, R=halogen), these latters being then condensed with suitable alcohols of the formula: ##STR3## wherein: R.sup.5 =H, CN, C.tbd.CH.
In above cited European Pat. Appl. there have also been described some processes for the preparation of the intermediates of formula II in which R=C.sub.1 -C.sub.4 alkoxy,
Amongst these processes, for instance, there may be cited the reaction between 1-alkoxycarbonyl-2',2'-dimethyl-cyclopropylmethyl-triphenylphosphonium bromide and a halosubstituted acrylic aldehyde, and the reaction between a haloallylphosphonate and caronaldehyde.